1. Field of the Invention
The present invention relates generally to a method of growing a selective area by MOCVD (Metal Organic Chemical Vapor Deposition).
2. Description of the Related Art
Monolithic integration of III-V group material compound semiconductor optical devices has been established as a fundamental technology for high-performance optical applications to fabrication of optical devices. This integration of technology makes possible the fabrication of multi-functional, high-performance devices, which was impossible with conventional technology that could go beyond the miniaturization or integration of devices. The integration of the III-V group devices is essential to the fabrication and operation of opto-electronic integrated circuits (OEICs), electro-absorption modulated laser (EML) optical amplifiers, and optical mode converters. Selective area growth (SAG) using MOCVD is generally used for the integration technology.
To fabricate a low-price optical part for use in an ultra high-speed optical transmission network, optical devices must be designed to have high optical coupling efficiency with the narrowest beam divergence as can be achieved from a semiconductor laser diode without a lens. For the purpose, an S SC-LD (Spot-Size Converter integrated Laser Diode) has been proposed in which a gain area in which a laser beam is emitted and a waveguide by which the laser beam travels without divergence are simultaneously fabricated through growth of a thin film in a selective area, in order to increase optical coupling efficiency and minimize optical loss between a laser diode and an optical fiber.
FIGS. 1A, 1B and 1C illustrate stages of an SSC-LD fabricating process, referred to for describing conventional MOCVD-based SAG
FIG 1A is a plan view illustrating SiO2 mask patterns 2 formed on an InP substrate 1. The width (W) of a window area 3 between the SiO2 mask patterns 2 is equal to that of a semiconductor layer to be grown in a selective area.
FIG 1B is a sectional view of the structure illustrated in FIG. 1A, taken along line A–A′. The semiconductor layer 4 is grown in the window area 3 by SAG based on MOCVD. FIG. 1C provides a conceptual illustration of an SAG mechanism. Referring to FIG. 1C, III-group source gases reacts with V-group source gases on the InP substrate 1 by vertical diffusion, lateral diffusion, and surface migration of the III-group source gases. Due to the surface migration, the III-group source gases, which is not deposited on the SiO2 mask patterns 2, migrates to the adjacent window and thus grows the thin film in the selective area.
This phenomenon, however, is more conspicuous at the boundary between the window area and the mask. In other words, the chemical reaction vigorously takes place at the edges of the window area by III-group source gases migrated from SiO2 mask in order to grow the semiconductor layer, so the growth takes place in greater numbers at the edge of the window thank in the middle of the window, thereby causing edge spikes (5 in FIG 1B) and changing the composition of the layer 4. The edge spikes refer to the increase of thickness at edges of a grown layer. Consequently, the surface migration affects the window at large, making it difficult to ensure uniformity in the thickness and composition of the grown thin film.
In the case of AlGaInAs laser diode having a larger conduction b and offset, the device exhibits excellent operational characteristics at high temperature, the SSC-LD having a high optical coupling efficiency is fabricated more easily in a BH (Buried Hereto) structure rather than in a RWG (Ridge WaveGuard) Structure, while if the AlGaInAs SSC-LD is fabricated in the BH structure, Al oxidation makes the fabrication of BH structure difficult.